If the MC is 6 and has 2 older brothers, that would be a minum 8 years before to the parents having the firstborn. If the grandparents are at their 40's (40~49), that'd mean they would be between 32 and 41 when they became grandparents. Divide that by 2 and you get 16~20,5 for each generation. So, if you consider they being in the latter part of their 40's, kinda young, but not that much (considering this would be a common thing among nobility), all in all, both generations would be arround their later teenager years though.The grandparents are in their 40's, the parents look to be in their 20's, and the oldest kid is...how old again? I feel like the math ain't mathing or it is mathing and they get down to business young.